How work translate=True in layout.label ? (Python Ui question)
There is no automatic translation, you will have to create a dictionary with the translations that is registered/unregistered through bpy.app.translations.register() and
bpy.app.translations.unregister(). The Manage UI Translations add-on can help you generate the tuples from which the dictionary is generated.

More information can be found in the manual and the wiki.